1. Field of the Invention
The present invention relates to switching regulators.
2. Description of Related Art
FIG. 13 is a diagram showing one configuration example of a non-isolated switching regulator using a photocoupler.
In the switching regulator shown in FIG. 13, a control circuit is driven by a voltage between VCC and IC_GND, monitors a voltage at monitor point P1, and turns On and OFF a switching device based on the result of the monitoring.
The switching regulator shown in FIG. 13 performs feedback control by directly monitoring the output voltage Vout; this allows, as shown in FIG. 14, the output voltage Vout to remain constant (at a set value) irrespective of the value of the output current Iout. That is, the switching regulator shown in FIG. 13 has high output stability.
However, a photocoupler is a relatively expensive component, and thus the switching regulator shown in FIG. 13 is unsuitable for achieving cost reduction.
Thus, from the perspective of cost reduction, non-isolated switching regulators using no photocoupler have been attracting attention. FIG. 15 is a diagram showing one configuration example of a non-isolated switching regulator using no photocoupler. A switching regulator similar to the switching regulator shown in FIG. 15 is disclosed in JP-A-2011-45174.
In the switching regulator shown in FIG. 15, a control circuit is driven by a voltage between VCC and IC_GND, monitors a voltage at monitor point P2, and turns ON and OFF a switching device based on the result of the monitoring.
The switching regulator shown in FIG. 15 performs feedback control without directly monitoring the output voltage Vout; this causes, as shown in FIG. 16, the output voltage Vout to vary, instead of remaining constant (at a set value), according to the value of the output current Iout. That is, the switching regulator shown in FIG. 15 has low output stability.
Thus, the switching regulator shown in FIG. 15 suffers from two problems. A first problem is that the output voltage Vout becomes high when the load is light, and a second problem is that the output voltage Vout becomes low when the load is heavy.
The first problem can be solved by providing a dummy load to avoid use under a light load. Providing a dummy load, however, poses another problem: increased standby power.
The second problem can be solved by increasing the electrostatic capacitance of a capacitor (an output capacitor C0) connected to the output terminal. Increasing the electrostatic capacitance of the output capacitor C0, however, poses another problem: increased cost of the output capacitor.